Successful management of laboratory monkey colonies requires a substantial investment of personnel as well as adequate facilities. The ultimate goal of colony management is to maintain the highest standards of health and well-being across all the monkeys in a given facility within the context of the research program. Despite the strides made in controlling colony diseases, in developing new housing procedures, and in modernizing facilities, some monkeys show abnormal behavior. Of particular concern is the small, but persistent percentage of monkeys that become self-aggressive and develop the syndrome of SIB. Although many causes have been suggested, none seem to explain why only a small percentage of monkeys is affected. The overall objective of this project is to characterize the nature of SIB in rhesus monkeys, and to identify the mechanisms responsible for the expression of these behavior patterns. The investigators will determine whether physical health or colony management practices differ between SIB and control monkeys, and will use archival procedures to ensure a sufficient number of subjects. The remainder of the work is focused on behavioral, biochemical, and pharmacological studies of a group of SIB and control monkeys. An evaluation will be made of the structure of SIB, its relationship to other behavior patterns, the context in which it occurs, and diurnal variation in SIB in order to identify stimuli in the environment that appear to provoke it. As part of this project, three risk factors will be examined that may have some association to SIB: hyperactivity, impulsive aggression, and arthritic disorders. The presence of such risk factors will be tested experimentally. Neurotransmitter correlates of these risk factors as well as the efficacy of drugs that may reduce SIB will be sought. Such a multilevel analysis will enable a characterization of this disorder, and will assist in determining what risk factors might predispose some monkeys to develop the syndrome. This information is critical for developing effective interventions and improving colony management.